Effects of Lattice Vacancies on Properties of LiBO₂ Material as Cathode Coating of Li-Ion Batteries

LiBO₂ is a wide band-gap insulator and a promising surface coating for stabilizing high-voltage cathodes in Li-ion batteries [1,2,3]. Despite its potential, uncertainties remain regarding the functional mechanisms of this coating [4]. Specifically, the transport of lithium ions and electrons through LiBO₂ in the presence of lattice vacancies is crucial for its design and development. This study employs density functional theory (DFT) calculations to investigate the effects of oxygen and boron vacancies on lithium diffusion and electronic band structures in both tetragonal (t-LBO) and monoclinic (m-LBO) polymorphs of LiBO₂ crystals. Our findings establish fundamental insights into this material and contribute valuable benchmarks for understanding insulator coatings in general. Regarding lithium diffusion, our study reveals distinct impacts of oxygen and boron vacancies on the energy barrier for lithium migration (<i>E</i>_m) in the two polymorphs. Oxygen vacancies decrease <i>E</i>_m in m-LBO but increase it in t-LBO, whereas boron vacancies significantly reduce <i>E</i>_M in both polymorphs, enhancing Li-ion diffusion coefficients. Analysis of electronic band structures using DFT indicates that both vacancy types introduce defect levels within the band gap, reducing the band gap (<i>E</i>_g) and transforming LiBO₂ into degenerate semiconductors. In conclusion, our study suggests that generating boron vacancies in LiBO₂ could potentially improve its lithium-ion conductivity. However, such vacancies may compromise the electronic insulation properties of the coating. Optimization strategies are therefore essential to achieve coatings with desired functional characteristics.<br/><br/><br/><b>Ackowledgment</b><br/>The authors acknolwedged the research fundings from the Materials Science and Engineering Institute, the University of Missouri-Columbia for supporting the computing resources for this work.<br/><br/><b>References</b><br/>1. Shan Gao et al. <i>Boron Doping and LiBO₂ Coating Synergistically Enhance the High-Rate Performance of LiNi_0.6Co_0.1Mn_0.3O₂ Cathode Materials</i>, CS Sustainable Chem. Eng. <b>9</b> (2021) 5322–5333.<br/>2. Xu-Dong Zhang et al. <i>An effective LiBO₂ coating to ameliorate the cathode/electrolyte interfacial issues of in LiNi_0.6Co_0.2Mn_0.2O₂ solid-state Li batteries</i>, Journal of Power Sources <b>426</b> (2019) 242-249.<br/>3. Mi Guo et al., <i>Excellent electrochemical properties of Ni-rich LiNi_0.88Co_0.09Al_0.03O₂ cathode materials co-modified with Mg-doping and LiBO₂-coating for lithium ion batteries</i>, New Journal of Chemistry <b>47</b> (2023) 968-2977.<br/>4. Shenzhen Xu, Ryan M Jacobs, Ha M. Nguyen et al,<i> Lithium transport through lithium-ion battery cathode coatings</i>, J. Mater. Chem A <b>3</b> (2015) 17248-17272